Cache pit diagram. Image credit: Meghan Howey.
By Natasha Blakely
Archaeologists in northern Michigan have used pulses of light shot from airplanes to double their discoveries.
This remote sensing technology is called light detection and ranging, or lidar. Lidar sends out a pulse of light that returns a measure of distance from the object it strikes. It can improve the efficiency of archaeological searches particularly when scanning vast areas for small details, according to a recent study published on PLOS ONE.
For example, lidar helped locate numerous cache pits in the upper Great Lakes region. In this case, a sensor was flown over the area being studied and the data was passed on to the researchers.
Cache pits were used by Native Americans to store food, tools and supplies between the years 1000 and 1600. These pits are roughly one meter in diameter and one meter deep, making only small changes in the overtly visible landscape. It is their more uniform shape and tendency to appear in clusters that separate the cache pits from naturally occurring changes in the landscape.
“I had always mistakenly thought the cache pits were largely correlated with living near the inland lakes,” said Meghan Howey, the main author of the study and an anthropology professor with the University of New Hampshire.
As a result, she previously looked around the lakeshores for the cache pits. But with lidar she found many cache pits far removed from the inland lakes, which was a shocking discovery, she said. She found 139 cache pit clusters with lidar, including 69 initially found without it.
“It made me think: if they’re there, what have I never looked at in terms of other things archaeologically?” Howey said. “That’s something I can 100 percent say I would never have figured out without lidar.
“When I say these things are small, you could barely see them when you’re standing right on top of them, in a dense forest,” she said. “They’re very subtle microtopography, so to be able to find them from a plane is pretty amazing.”
Cache pits are remnants of history that affect the area’s topography in subtle ways that are hard to detect. But with lidar these small scale archaeological discoveries are no longer so hard to find.
Lidar hit Howey’s radar through Jason Tallant, a data manager and research scientist with the University of Michigan Biological Station near Pellston. Lidar was used at the station to look at the forest canopy and underlying land surface. When the researchers discovered some cache pits, Tallant told Howey.
“Sure enough,” Tallant said. “We could see all the known locations but then we were also seeing these other locations that looked very similar but were unknown. As of five years ago, when they did this initial survey work, they thought they had found all of the pre-European settlement Native American cache pits in the region and we found a number of new sites.”
Lidar is not new to archaeology. Remote sensing has been used to find archeological sites in places without forests for years. The Smithsonian used it on Mayan ruins and in Cambodia, said Michael Palace, a professor of environmental science at the University of New Hampshire, also involved with the project.
“What we’re saying is that’s been done a lot,” Palace said.
What makes this study stand out from the others was the way lidar was used to look for archaeological features on a small scale. Most archaeologists use lidar on a much larger scale.
In this case, Howey wasn’t looking for pyramids or giant ruins, but small features built by low density societies. Other archaeologists had characterized those small features as not that complicated or not leaving much of a signature, Howey said.
“Well, there you go,” Howey said. “Pretty interesting signature on the landscape that we’ve missed for years.”
Howey did not disclose the locations of what they found in the study or to people not involved in it. What they found was amazing and interesting but ultimately meant for researchers, archaeologists and the tribal communities these artifacts belong to, Howey said. To preserve these archaeological sites from raiders and vandalizers, the locations were not revealed.
It’s a new way of documenting pre-European settlements and their impact on the landscape, Tallant said. As a footprint of native people on the land that has cultural and historical relevance, it needs to be protected and inventoried.
The code used for the lidar, however, is free and available for the public to access. They want other people to get inspired and apply it to their areas, Howey said.
“At the University of Michigan Biological Station, we are really embracing an open science approach,” Tallant said. “Any data we collect on our own, we try to make as publicly available as possible.”
It’s part of a new era of science, said Palace, to share methods and engage in transparency. It allows for more criticism, but also for people to use and expand on it.
The data for the study and other research the University of Michigan Biological Station is involved in is available online.